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The radiometer tracks the sun's progress across the Manhattan skyline and sends a signal from the roof to the command computer on a floor 90 meters below. Blinds fall slowly with the buzz of an electric motor, cutting off the sun's glare on computer screens. Another computer triggers the shades on the opposite side of the building to rise while another system shuts off the air-conditioning and adjusts the internal lights.

The New York Times Co. saves energy at its 52-story headquarters using the oldest lighting technology in the world: the sun. Floor-to-ceiling windows let sunlight flood into the office space and sensors then dim the internal lights to save energy. In the process, compared with other buildings in New York City, the Times Building has reduced its energy use by 24 percent, according to a new report prepared by Lawrence Berkeley National Laboratory (LBNL).

Letting the sun do the work of lighting up buildings is obvious. It's cheap, it's free and it's as easy as a window. Or, as managing director of Sustainable Energy Partnerships Adam Hinge says, "there are lessons we can relearn" from the building practices of the time before cheap fossil fuels and ubiquitous air-conditioning. As it stands, the energy used to light, cool and vent the buildings of the world's cities accounts for roughly 40 percent of humanity's carbon dioxide emissions, the greenhouse gas primarily responsible for climate change.

But using daylight turns out to be more complicated than building floor-to-ceiling windows. A modern building in a city like New York requires specific glazing on its windows to control glare as well as some form of shade to block at least some of the sunlight and enable employees to see their computer screens. An energy-efficient system requires dimmable lights that must be affordable, long-lasting and easy to maintain. And the people using the building must like the system—or at least find it easy to control.

In a bid to gain a better understanding of all those factors, the Times built a full-scale model of 400 square meters of the building in College Point, Queens, to test various systems before going ahead with final construction in Manhattan. Even then, outfitting the Times’s 20 floors of office space with daylighting equipment constituted "the largest direct procurement of innovative lighting and shading technologies in the U.S.," according to the LBNL report.

New York City boasts some 10 percent of all the office space in the entire U.S.—more than 50.1 million square meters—and could save $70 million a year in power costs, or roughly 340 gigawatt-hours of electricity, by relying more on sunshine (as well as even simpler fixes like turning off the lights that are not needed at night.) That's according to another recently released report dubbed "Let There Be Daylight" from Green Light New York, an advocacy group, which notes that more than a quarter of the energy used in New York City's buildings goes to interior lighting, which is often used even in the middle of a sunny day.

All the way back in 1977, when LBNL's buildings guru Stephen Selkowitz began working on energy-efficient construction, his very first project advocated the use of more daylight. Yet, in the 35 years since then the trend has been in the opposite direction. "I'm a failure, because we should have solved the problem by now," he says. "It has not been scalable," meaning the lessons learned in one building have not been translated into other similar buildings or even other cities.

The Times Building is an example of that as well. Whereas the company itself employs a sophisticated daylighting and energy savings system, it only inhabits slightly less than half of the 140,000-square-meter building. The remaining space is rented out to tenants by co-owner Forest City Ratner—and not all the tenants opt for such systems, which can cost from $2 to $10 per square foot (0.09 square meter) of office space.

Of course, that cost does deliver roughly three kilowatt-hours of energy savings per square foot per year, by Selkowitz's analysis of the Times Building, or roughly $13,000 saved annually per floor. That's "pretty darn good," he notes. But building managers are often skeptical. Even New York Times facilities director Patrick Whelan thought the new system, especially the under-floor air-circulation vents, would be a "nightmare" when the company moved in back in 2007. (Under-floor vents save energy by requiring fewer pumps to move the air as well as relying on the natural warming of the internal building air to allow circulation. Cold air comes up from floor, warms and rises to the ceiling.)

"Basically, things are working really well," Whelan says. The under-floor vents proved easier to access and quieter than traditional pumped vents in the ceiling and, in five years, only 5 percent of the energy-saving, dimmable fluorescent lights have had to be replaced—proving that the bulbs are durable. "To tell you the truth, we get very few complaints," he adds.

Yet, thanks to new buildings rising to the north and west, the sophisticated system now has to be retrained to deal with unexpected glares off of new windows. That requires a comprehensive study of reflections and then reprogramming the computer control system. In the end, although using sunshine seems easy, "you can't fall out of bed and do this by yourself," Selkowitz says.